Microstructure of Nanocrystalline Yttria‐Doped Zirconia Thin Films Obtained by Sol–Gel Processing

Abstract

J Ernst Ruska-Centrum fu¨r Mikroskopie und Spektroskopie mit Elektronen, Forschungszentrum Ju¨lich, 52425 Ju¨lich, GermanyNano-and microcrystalline yttria-stabilized zirconia (YSZ) thin films with a dopant concentration of 8.370.3 mol% Y 2 O 3 were prepared with a variation in grain size by two orders of magnitude. A sol-gel-based method with consecutive rapid thermal annealing was applied to fabricate YSZ films, resulting in about 400 nm YSZ on sapphire substrates. The average grain sizes were varied between 5 nm and 0.5 lm by heat treatment in the temperature range of 6501-13501C for 24 h. High-resolution (HRTEM) and conventional transmission electron microscopy analyses confirmed specimens-irrespective of the thermal treatment-consisting of cubic (c-)ZrO 2 grains with nanoscaled tetragonal precipitates coherently embedded in the cubic matrix. Energy-dispersive X-ray spectroscopy and HRTEM on a large number of specimens yielded a homogeneous yttria concentration within the grains and at the grain boundaries with the absence of impurities, i.e. silica at the grain boundaries.

Microstructures of YSZ and CGO Thin Films Deposited by Spray Pyrolysis: Influence of Processing Parameters on the Porosity

“…Between 300 °C and 800 °C, the porosity ranged between 10 vol% and 30 vol%. Peters et al13 and Butz et al15 found a porosity of 15 vol% and 8 vol% by TEM for spin‐coated sol‐gel YSZ thin films annealed at 650 °C and 850 °C, respectively.…”

“…For vacuum techniques, the thin films are deposited directly from solid targets resulting mostly in crystalline films; whereas for methods employing liquid or gaseous organic‐precursors, the films are predominantly amorphous after deposition. YSZ thin films prepared with the latter are reported to develop porosity during post‐deposition thermal treatments 13, 15–22. For example, YSZ thin films deposited by sol‐gel routes show ∼15 vol% porosity after annealing at 650 °C for 24 h, with pore sizes similar to those of the grains 13, 15.…”

“…YSZ thin films prepared with the latter are reported to develop porosity during post‐deposition thermal treatments 13, 15–22. For example, YSZ thin films deposited by sol‐gel routes show ∼15 vol% porosity after annealing at 650 °C for 24 h, with pore sizes similar to those of the grains 13, 15. Pores were even observed in zirconia‐based nanoparticles derived from metalorganic precursors 23–26.…”

“…Pores were even observed in zirconia‐based nanoparticles derived from metalorganic precursors 23–26. Qualitative analysis by scanning or transmission electron microscopy and atom force microscopy of YSZ thin films prepared from metalorganic precursors revealed pore sizes in the range of 1 nm to 3.5 nm in films annealed at 600 °C 13, 15–19. Fully dense films were obtained only after annealing above 1200 °C.…”

Chemical Solution Deposition Technique of Thin-Film Ceramic Electrolytes for Solid Oxide Fuel Cells

“…The success of this process was established with the achievement of 1.0 V OCV at 650°C [31]. Numerous significant progresses across the globe are discussed in various articles [3,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46].…”